Tires with a radial carcass, commonly known as “radial tires” are gradually becoming the norm in most markets, particularly in the passenger vehicle tire market. This success is due in particular to the durability, comfort, lightness and low rolling resistance that radial tire technology enjoys.
The radial tire is essentially made up of flexible sidewalls and of a more rigid crown, the sidewalls extending radially from the beads as far as the shoulders, the shoulders between them delimiting the crown, the crown supporting the tread strip of the tire. Because each of these parts of the tire has its own specific functions, it also has its own special reinforcement. One feature of radial tire technology is that the reinforcement of each of these parts can be precisely adapted relatively independently of each other.
The crown reinforcement of a passenger vehicle radial tire (commonly known as a “passenger car tire”) comprises, in the known way, the following elements:                a radial carcass reinforcement formed of reinforcing elements (generally textile) connecting the two beads of the tire,        two crossed crown triangulation layers (or plies) essentially consisting of reinforcing elements (generally metal) each forming an angle of about 30° with the circumferential direction of the tire,        a crown belt essentially consisting of reinforcing elements practically parallel to the circumferential direction of the tire, often known as 0° reinforcing elements even though in general they make a non-zero angle with the circumferential direction, for example an angle of between 0 and 10°.        
In broad terms, the carcass can be said to have the prime function of containing the internal pressure of the tire, that the crossed plies have the prime function of giving the tire its cornering stiffness and that the crown belt has the prime function of resisting centrifugal effects on the crown at high speed. Further, interaction between all these reinforcement elements creates what is known as the crown triangulation. It is this triangulation that gives the carcass its ability to retain a relatively cylindrical shape in the face of the various stress loadings.
Each of these elements of the crown reinforcement is generally combined by calendering with rubber compounds. The stack of these elements is then joined together during the vulcanising of the tire.
After several decades of research, progress and development of radial tire architecture, it is the combination of all these reinforcement elements (carcass, crossed layers, belt) that allows the radial tire to achieve the undeniable comfort, long life and cost performance that has made it the success it is. Throughout this development, attempts have been made to improve the performance of the tires, for example in terms of their mass and their rolling resistance. Thus the crown of radial tires has gradually reduced in thickness as increasingly high-performance reinforcing elements have been adopted and increasingly thinner layers of calendering rubber have been used so that tires that are as light as possible can be manufactured.